The present invention relates to systems for controlling the venting of fuel vapor from a fuel tank and particularly from an on-board motor vehicle fuel tank. Currently, fuel vapor emission control systems are required on light truck passenger motor vehicles. Fuel tanks for such vehicles are often molded of plastic material and configured to conform around structural members of the vehicle such as stiffener members for the vehicle undercarriage or body floor. This often results in the upper or top wall of the tank having a valley formed therein often running longitudinally with respect to the vehicle chassis and which effectively divides the vapor dome within the tank into two or more compartments when the fuel level is not less than that of the lowest level of the valley.
This compartmentalized vapor dome within the tank has caused problems in providing venting of the fuel vapor from the tank and has resulted in the need for a plurality of vapor vent valves with one valve provided in each separate compartment of the vapor dome.
Where the fuel vapor vent valves are float operated and are installed in the tank externally through access openings in the upper wall of the tank, it has proven costly and cumbersome to provide the interconnection of the plurality of vent valves to the remote vapor storage device such as a charcoal filled canister. Furthermore, where the tank has a trough or valley formed in the upper surface thereof, it has been required to provide draining of the liquid fuel from the vent valves and lines when the fuel level falls below the lowest level of the valley upon withdrawal of fuel from the tank.
Thus, it has been desired to provide a way or means of eliminating the need for access openings in the tank wall to install vent valves and to minimize the number of conduit and interconnections thereof required to provide venting of the compartmentalized vapor domes in the fuel tank and to insure drainage of the liquid fuel from the vent system in order to prevent blocking of vapor flow to the storage canister.
Referring to FIG. 2, a known system has the fuel tank indicated generally at 1 which has an upper wall having an upper level 2 and a lower level 3 such that a separate vapor dome 4 is formed within the tank when the fuel rises above the undersurface of the level 3.
A first vapor vent valve 5 is disposed within the vapor dome 4 adjacent the undersurface of the upper level 2; and, a second vapor vent valve 6 is disposed adjacent the undersurface of the tank top level 3 and the outlets of the respective valves 5, 6 are interconnected by a conduit 7 which passes beneath the undersurface of the lower level 3. A second conduit 12 is connected to conduit 7 through an access opening 8 in the lower level 3 of the upper wall; and, conduit 12 is connected to a vapor storage canister 9 which has an outlet 10 adapted for connection to the air inlet of an engine. The canister 9 typically has a purge air inlet 11 for admitting atmospheric air to purge the canister upon engine startup.
The present invention relates to vapor venting of fuel tanks such as for motor vehicles and particularly relates to fuel tanks having a multilevel upper wall and more particularly to tanks having a valley formed in the upper wall for conforming to structural members of the vehicle and thus having a compartmentalized vapor dome. The present invention provides for vapor vent valving in each compartment of the vapor dome interiorly of the tank to eliminate external hose connections along the outer surface of the tank top. The system of the present invention employs a vapor vent valve in each vapor dome compartment and the vent valves are disposed completely interiorly of the tank with the outlets interconnected; and, a single vapor vent line exits through the upper wall of the tank for connection to a storage canister. The interconnecting lines within the tank include a drain valve disposed at the lowest level of the lines passing under valley formed in the upper tank wall. In one embodiment of the invention the drain valve is a one-way pressure operated valve and in an alternate form the drain valve is float operated.